A federal judge has temporarily barred the District from enforcing part of its recently passed law requiring cautionary labels on "flushable" wet wipes, saying the city's approach probably violates the First Amendment.

Judge James E. Boasberg of the U.S. District Court for the District of Columbia on Friday issued a preliminary injunction that prevents officials from enforcing the law against a single wipes manufacturer, Kimberly-Clark. The law, which takes effect Jan. 1, can still be applied to other companies that were not involved in the lawsuit.

D.C. Council Chairman Phil Mendelson (D) said he was surprised by the ruling, because courts have repeatedly upheld laws that mandate labels disclosing information such as the cancer risks of smoking or the sugar content of snacks.

"It's no more of a First Amendment issue, I would think, than telling tobacco companies what they have to put on packages of cigarettes," Mendelson said.

Kimberly-Clark did not respond to requests for comment. D.C. Attorney General Karl A. Racine (D), whose office is defending the city in the suit, could not be reached for comment.

Boasberg's 30-page written opinion struck a lighter note over the wipes controversy, which has become an unlikely crucible for broad questions about corporate speech, consumer rights and regulatory overreach.

"Lurking beneath this city's streets lies a purported scourge of our sewer system," the ruling begins, invoking the threat of certain kinds of wet wipes that "unwitting consumers might blithely flush" but that "bind together in the subterranean realm." He later added that his decision did not mean "the District's 'Protect Your Pipes' campaign is a pipe dream."

The law is intended to remedy a problem city officials find far from amusing. The District's sewer agency — and other utilities across the United States — say that wipes that do not disintegrate can clog the sewer system and attract grease and oils into pipe-obstructing "fatbergs" that cost tens of thousands of dollars to clear.

While the city's legislation does not ban such wipes, it requires them to pass a test to determine that they will properly dissolve in the sewer. If the product fails, its manufacturer must label the package with an indication that it should not be flushed.

Wipes have fueled a growing industry in recent years. Niche operators have sprung up, such as Dude Wipes, founded in 2011 by an all-male cohort of recent college graduates.

In its lawsuit, filed earlier this year, Kimberly-Clark alleged that the District's law was unconstitutional because it sought to regulate businesses outside the city and would force companies that considered their wipes to be flushable to label them otherwise.

Boasberg found that the law "likely treads impermissibly" on the company's right to free speech.

While the courts have upheld the constitutionality of nutritional labels as well as other types, Boasberg noted, the facts on such labels were generally not in dispute.

By contrast, Kimberly-Clark maintained that its wet wipes could safely be flushed.

"It is true that the FDA, for instance, could require Hostess to disclose the calorie count of Twinkies, even if the company's marketing arm might prefer otherwise," Boasberg wrote. "But it cannot require that company to tell consumers its sugary treat 'should not be eaten' nor ban it from labeling that product 'edible.' "

Boasberg said that he would revisit the law's constitutionality after the District drafts regulations for specifics on what the labels it requires will look like and say.